1. Field of Invention
The present invention relates to an arrangement for detecting the angular position of a rotatable part, for example, a printing head or other part of an office machine.
2. Description of the Prior Art
An arrangement is known wherein detection of the angular position of the rotating part is effected by means of a disc rigidly connected to the rotatable part itself and having on a first circumferential track thereof as many cut-outs as there are angular positions in which the rotatable part can be positioned. These cut-outs co-operate with a first light-sensing unit which detects the passage thereof and generates a corresponding electric signal for each elementary angular movement of the rotatable part. In this arrangement, for phasing of the electric signals generated by the first light-sensitive unit and for generating a further electric signal at each complete revolution of the rotatable part, a further cut-out is provided on a second circumferential track of the disc or of a second disc keyed to the first. A second light-sensing unit co-operates with this further cut-out.
This arrangement has the disadvantage that if there are many angular positions to be detected, and therefore if the elementary angular movement is of a few degrees, there are also many cut-outs along the first cirumferential track of the disc and, therefore, since they must be spaced sufficiently from one another to give the light-sensing unit the means of detecting them individually, the diameter of the disc becomes very large and the arrangement becomes cumbersome.